The sail to Long Island Sound is not so bad
While I agree with the posts talking about spending time in the Delmarva/Chesapeake areas, I would disagree with the first respondent on one point. I sailed my boat from Cape May to Sag Harbor and it was a little over 1 1/2 days sailing time. It wasn't that bad, and on a cruise of that length having a couple of 24 hour+ sails is not a big deal. If you go to Montauk or Block Island directly, you will be set up for amazing cruising grounds.
I used to keep my boat in Sag Harbor, and am familiar with many of the cruising choices. Within one day's sail you have the following (only a partial list): Montauk, Sag Harbor, Greenport, Dering Harbor and Cochles Harbor of Shelter Island, Old Saybrook, Mystic, Stonington, Branford, Port Jefferson, Block Island, Fishers Island, and of course Newport. From Newport, you open up the chain of the Elizabeth Islands (especially Cuttyhunk) off Woods Hole, Cape Cod, Martha's Vineyard and Nantucket. I have left out more places than I have included. The only negative is that some of these places start to get a bit cool in September and October (depends on how adaptable you are to that).
Alternatively, you can go up the coast of NJ, in to the port of NY and work your way to the Western side of LIS and head east. The western ports are not quite as interesting as the eastern ones, but you still have a few nice stops such as City Island, Port Washington, Mamaroneck, Glen Cove, and maybe Huntington before you reach some of the spots I mentioned above. Not all of the western ports are as well configured for transients as the western part of LIS
It's possible that you would have a great trip just exploring the Chesapeake, because there are a lot of great sights there. , I'm not aware of many great spots in the Delaware until you reach Cape May. If you feel you want to extend to LIS and/or Southern New England - don't fret the trip north of Cape May. Just keep on top of the weather forecasts, because we do get hurricanes and other storms in the northeast too!
Either way you do it, have a great trip. I'm jealous already!!!!